Flood Consequence Assessment. Proposed Student Accommodation, East Bay Close, Cardiff

Transcription

1 Proposed Student Accommodation, East Bay Close, Cardiff Client By KDP Architects RVW Consulting 13 Seymour Terrace 6 Neptune Court Liverpool Vanguard Way L3 5PE Ocean Park Cardiff CF24 5PJ Tel: Fax: B D A Stimpson S C Walrond 6 October 217 Revision Author Approved Date

2 RVW Consulting Limited CONTENTS 1. Introduction 2. Brief 3. General 4. Acceptability Criteria 5. Conclusion 6. Planning Drawings 7. Tan 15 Development Advice Map and Flood Level Information Project Number C6622

3 RVW Consulting Limited 1. INTRODUCTION RVW Consulting Limited has been commissioned by KDP Architects to undertake a flood consequence assessment for a project at East Bay Close, Cardiff. The assessment has been undertaken to support a planning application to construct a student accommodation development at the site. Where possible, the assessment has been developed in conjunction with Natural Resources Wales. This assessment has been prepared broadly in line with the recommendations set out in Technical Advice Note 15 (TAN 15) Development and Flood Risk, published by the National Assembly for Wales in July BRIEF We have been instructed to provide an initial assessment of the flood risks associated with the site, and whether the development can be justified in terms of TAN 15. As part of the assessment we have visited the site to consider the likely implications of the proposed development. We have also contacted Natural Resources Wales to seek their views regarding the flood risks associated with sites in this area. In addition, this assessment contains specific flood level information for the site that has been provided by Natural Resources Wales. Project Number C6622

4 RVW Consulting Limited 3. GENERAL Background KDP Architects are promoting a project to construct a student accommodation development at East Bay Close, Cardiff. The outline development proposals have been discussed with the Local Planning Authority, who is satisfied, in principle, with the scheme. Site Location The proposed site is located to the east of Cardiff town centre, and part of the site is located beneath the A4234 Central Link. The site is currently comprised of car showroom buildings, access roads and parking areas, soft landscaping, hardstandings and gravelled areas. History The site currently operates as a car sales premise. The site was previously operating as a commercial garage since the early 199s. Development Proposals The development proposals for the project comprise the construction of a ten-storey student accommodation building with associated access roads, car parking, and hard and soft landscaped areas. These details are illustrated in the planning drawings contained in Section 6.. Drainage The development proposals will result in a minor decrease of the impermeable area offered by the site. To ensure that there will be no flood risk due to surface water generation; SuDS will be used to dispose of all new surface water flows from the proposed development site. The SuDS design will be investigated in more detail during the detail design phase, and will comply with the sustainability aspirations of the LPA and Client. Foul flows generated by the existing site premises are assumed to connect to the adjacent public combined sewerage system. Foul flows generated by the development proposals will also connect to the adjacent public combined sewerage system, using new foul drainage from the site. As the public combined sewerage network is maintained by Dwr Cymru Welsh Water, the risk of foul drainage flooding at the site is considered to be very low. Project Number C6622

5 RVW Consulting Limited Flood Defences There are formal flood defences in place that protect the Cardiff area. The Cardiff Flood Alleviation Scheme was constructed between 198 and 1983, following the floods of December It consists of defences along the banks of the River Taff, from Llandaff Weir to Clarence Bridge. The Cardiff Scheme was designed and constructed prior to the implementation of the Cardiff Bay Barrage Scheme, when tidal influence directly affected river levels as far upstream as Blackweir. Flood levels over this length of the river were determined by a combination of fluvial flows and tide level. Upstream of Blackweir flood levels are only dependent upon river flow. At the downstream end, in the vicinity of Grangetown, even for extreme river flows, highest flood levels were influenced by the tide. The highest recorded tide in Cardiff at the time was 7.8m, and defences were set at a minimum of 8.3m AOD, which provided a.5m freeboard on the highest tide. Flood defence levels are then increased upstream determined by the design flood flow in the river. Since construction of the Cardiff Bay Barrage the direct tidal influence on river levels has effectively been removed. Flood levels downstream of Clarence Bridge are now determined by the water level in Cardiff Bay. The Cardiff Bay Barrage is a total exclusion barrage, in that seawater is prevented from entering at any time. The bay water levels during a flood are determined by river flows from the River Taff and River Ely entering the bay during a tide-lock scenario, when the sluice gates are closed to prevent ingress of seawater. Even for extreme combinations of surge tide and river floods, the maximum level in the bay is calculated to be lower than the 7.8m tide level used for the design of the scheme. The Cardiff Bay Barrage Scheme provides a minimum standard of tidal flood protection for the.5% flood event scenario (1 in 2 year return period). Site Topography The proposed site is generally flat, with an average ground level of 7.9m AOD. The site possesses existing ground levels ranging from circa 7.6m to 8.4m AOD. Proposed Levels Due to the risk of flooding from coastal processes, the proposed FFL of the student accommodation building will be set at 8.85m AOD. This will ensure that the building will remain flood free for the lifetime of the development (up to the year 2117) and this FFL also includes an element of freeboard (25mm). It is anticipated that proposed levels would be similar to existing levels, for the main body of the external site, to ensure that the proposals tie-in with existing features, boundaries, and access roads already constructed to service the development. Project Number C6622

6 RVW Consulting Limited Flood Levels The main source of flood risk to this area is coastal flooding from the Cardiff Flats to the south-east during a breach of the sea defences. Based on the predicted sea levels at the Cardiff Flats, the site could be at risk of flooding for the.5% and.1% flood event scenarios. Over the course of the development lifetime (1 years), this risk will increase due to the effects of climate change. This information is illustrated on the Natural Resources Wales flood map and flood level information for the area, a copy of which is contained in Section 7.. The predicted extreme sea level at the closest tidal node for the.1% flood event scenario for 2117 is 1.2m AOD, and this figure includes a climate change allowance for sea level rise over the lifetime of the development. As the coastal defences that protect the Cardiff Flats are maintained by Natural Resources Wales, and the development site is approximately 2,5m from the coastline the risk of flooding at the site is considered to be very low. Flood History There is no record of flooding at the site. TAN 15 Classification The specific guidance with regards to the classification of student accommodation contained in the TAN 15 Document (Figure 2) confirms that the proposed development could be classified as highly vulnerable development. The TAN 15 Development Advice Map for the area indicates that part of the site would be categorised as a Zone C1 area. Zone C2 classifies the site to be served by significant infrastructure, including flood defences. Flood Risk The main source of flood risk to this area is coastal flooding from the Cardiff Flats to the south-east during a breach of the sea defences. Over the course of the development lifetime (1 years), this flood risk will increase due to the effects of climate change. As the coastal defences that protect the Cardiff Flats are maintained by Natural Resources Wales, and the development site is approximately 2,5m from the coastline the risk of flooding at the site is considered to be very low. Project Number C6622

7 RVW Consulting Limited If required, the flood risk could be further mitigated by establishing a flood management plan for the development site. This could include the preparation of formal flood plans and procedures as part of an operating plan for the premises. In addition, this may include the erection of suitable warning signs to inform people entering the site, and the development of safe and effective flood warning and evacuation plans agreed with the local authority and emergency services, including subscription to Floodline Warnings Direct (as itemised in Appendix 6 of TAN 15). Flood warnings are usually issued by the Natural Resources Wales with an effective lead-time of between 12 and 24 hours before the onset of flooding around the site. Natural Resources Wales provides a comprehensive flood warning service for the River Ely. Warnings are issued to the Emergency Services, the Media and, other than for Flood Watch, to individual properties within Flood Risk Areas via the Floodline Warnings Direct service. Floodline Warnings Direct is a free 24-hour service to registered users providing automated warnings to telephone, mobile, fax or pager. The 24 hour Floodline number is a telephone information service operated by the Natural Resources Wales in Wales. Trained operators provide a 24/7 service to provide immediate advice on flood risk. They also provide a Quickdial number that allows direct access to any recorded flood warnings for the local area. Project Number C6622

8 RVW Consulting Limited 4. ACCEPTABILITY CRITERIA Whilst it is understood that the majority of the proposed development site is not located within the flood zone, in support of the planning application, the following information is offered. 1. The proposed development will generate no flood risk, due to increased surface water run-off, as SuDS will be used to safely manage surface water disposal. 2. There will be no loss of flood storage. 3. Flood defences are those that currently exist, and are deemed adequate for existing usage. 4. The Client is aware of the limited potential for flooding in this area and will implement flood management procedures, if required. 5. If considered necessary, end users and occupiers will be informed of the potential flood risk at the site so that they are aware of their duties under the Health and Safety at Work legislation, and can be duly made aware of any appropriate procedures to protect people and property. 6. Escape routes onto adjacent higher land and buildings, which are deemed to be outside the extent of the flood risk zone, are available. 7. If considered necessary, formal flood plans and procedures can be established as part of an operating plan for the premises. This could include the erection of suitable warning signs to inform people entering the site, and the preparation of safe and effective flood warning and evacuation plans agreed with the local authority and emergency services, including subscription to Floodline Warnings Direct (as itemised in Appendix 6 of TAN 15). 8. Flood proofing and mitigation will be considered within the design of the development, if considered necessary namely: raising electrical sockets/appliances, using hard flooring and rugs instead of carpets, lime plaster instead of gypsum, non-return valves fitted to pipes etc. This could be undertaken in accordance with the guidance that is available from the Environment Agency using their online publication Prepare your property for flooding. Project Number C6622

9 RVW Consulting Limited 5. CONCLUSION The size and nature of the proposed development can be categorised as highly vulnerable development in accordance with TAN 15. Due to the nature of the development, the proposals do not aggravate or increase the risk of flooding to the existing site or to surrounding properties. The Client has been advised of the very limited potential for flooding in this area and is aware of the residual risk. In summary, based upon the published guidelines and relevant provisions of the technical advice note, the proposed development meets the acceptability criteria. Project Number C6622

10 RVW Consulting Limited 6. PLANNING DRAWINGS Project Number C6622

11 :3 :31 :32 12 :33 : :3 : Stair Core C :36 :28 Up :27 15 :37 :38 :26 :39 : Lift 4 :4 15 :2 :41 e Stor : :43 : :54 :44 1 :45 :53 : :22 11 : :46 : : :21 :56 :49 : Lift :2 : Up D 24 unal e ng Comm/Lou en 6 Kitch L: Dow n Core :47 Stair :5 al e mun Com /Loung en Kitch L:5 unal e ng Comm/Lou en 7 Kitch L: al mun nge Com /Lou en Kitch L:8 :19 :18 :59 :6 :17 :11 unal e Comm/Loung en 4 Kitch L: :12 :13 :61 :14 :16 al e mun Com /Loung en Kitch L:3 : : Lift :1 t Plan Room 9 : itch Sw om Ro AREA TO REMAIN UNDEVELOPED (Hatched Pink) :8 12 ma Cine om Ro : ting Mee 2 Room :6 623 eting 1 Me Room e Stor 12 Up 18 Post Stair IT Suite Core B dry.c sw Laun Di 154 na Gym sium e Stor :1 :5 Bin ore St ption Rece r nage Ma :2 :4 e Lift 165 Offic Up 17 Stair A Core unal e ng Comm/Lou en 2 Kitch L: Y LA Dow n :3 SEP1A unal e Comm/Loung en Kitch L:1 Y LIT SP IBI 2.4 DROP OFF 3m x4 VIS EXIT PARKING ZONE 2.4 x 43 mv ISIB 61 ILIT YS PLA Y VISITORS PARKING (32 no.) Proposed Site Plan Scale 1:5 All dimensions to be checked on site. Figured dimensions to be read in preference to scaled. KDP accepts no responsibilty for any unauthorised amendments to the drawing and does not permit unauthorised copying of the drawing. This drawing is copyright and remains the property of KDP unless otherwise agreed. A B C D E F G H I J SCHEME REVISED SCHEME REVISED Scheme Revised following comments from LPA Amendments to Landscaping Additional Cycle spaces added Amendments to Car Park Bin Store amended Landscape amended Cycle Spaces amended Landscaping amended CW CW CW CW THE KEITH DAVIDSON PARTNERSHIP CHARTERED ARCHITECTS - PROJECT MANAGEMENT - 3D VISUALISATION 13 Seymour Terrace Seymour Street Liverpool L3 5PE Telephone: +44 () Facsimile: +44 () info@kdparchitects.com Website: Planning Client Job number Job title Drawing number Eastbay Close, Cardiff CF14BA Drawing title Proposed Site Plan Revision 1437 J 11 Scale Drawn 1:5@A1 CW Checked Date

12 Communal Kitchen/Lounge L:3 Communal Kitchen/Lounge L:4 :1 1A Communal Kitchen/Lounge L:2 :4 :5 Store Stair Core B Up Up Communal Kitchen/Lounge L:1 :1 Store Switch Room :54 Dis W.C. Manager FF PO 19 Up P L AY Stair Core A :47 :45 DR O Bin Store IT Suite :44 : PARK ING :43 :49 ZO Post NE Office Reception Meeting Room 1 Meeting Room 2 :51 :5 :41 : :4 :52 Gymnasium Cinema Room :39 :53 Laundry Plant Room :3 :2 :61 :6 :59 Communal Kitchen/Lounge L:8 Communal Kitchen/Lounge L:7 :58 :57 :56 :62 :55 Store :36 :37 15 : Lift Down Stair Core D :46 Up IL I TY S 12 PLAY S Y T I L I SIB x 43m VI :9 : :16 :23 Lift :17 :18 :19 Communal Kitchen/Lounge L:5 Communal Kitchen/Lounge L:6 :2 :21 :22 :15 :24 SEP :25 :14 :7 :8 :13 :26 :27 :12 :28 :11 :29 :3 :31 :32 : : : Stair Core C 12 Lift Lift Down SI B x AR E UN A TO RE D (Ha EVEL MAIN O tch ed PED Pin k) VIS I PA TORS RK (32 ING no. ) m VI EXIT 61 Proposed Site Plan Scale 1:2 All dimensions to be checked on site. Figured dimensions to be read in preference to scaled. KDP accepts no responsibilty for any unauthorised amendments to the drawing and does not permit unauthorised copying of the drawing. This drawing is copyright and remains the property of KDP unless otherwise agreed. A SCHEME REVISED B C D E F G H I Scheme Revised following comments from LPA Landscaping Amended Additional cycle spaces added Amendments to Car Park Bin Store Amended Landscaping amended Cycle Spaces amended Landscaping amended CW CW CW THE KEITH DAVIDSON PARTNERSHIP CHARTERED ARCHITECTS - PROJECT MANAGEMENT - 3D VISUALISATION 13 Seymour Terrace Seymour Street Liverpool L3 5PE Telephone: +44 () Facsimile: +44 () info@kdparchitects.com Website: Planning Client Job number Job title Drawing number Eastbay Close, Cardiff CF14BA Drawing title Proposed Site Plan Revision 1437 I 12 Scale Drawn 1:2@A1 CW Checked Date

13 ELE C SECTION B-B 3mm Floor to Floor SECTION A-A 3mm Floor to Floor ELE B ELE D 3mm Floor to Floor EIGHTH FLOOR SEVENTH FLOOR 3mm Floor to Floor SIXTH FLOOR 3mm Floor to Floor FIFTH FLOOR 3mm Floor to Floor ELE A FOURTH FLOOR Key Plan Scale NTS 3mm Floor to Floor THIRD FLOOR 3mm Floor to Floor SECOND FLOOR 3mm Floor to Floor FIRST FLOOR 355mm Floor to Floor GROUND FLOOR Proposed Front Elevation (ELE A) Scale 1:2 3mm Floor to Floor 3mm Floor to Floor EIGHTH FLOOR 3mm Floor to Floor SEVENTH FLOOR 3mm Floor to Floor SIXTH FLOOR 3mm Floor to Floor FIFTH FLOOR 3mm Floor to Floor FOURTH FLOOR 3mm Floor to Floor THIRD FLOOR 3mm Floor to Floor SECOND FLOOR 3mm Floor to Floor FIRST FLOOR 355mm Floor to Floor GROUND FLOOR Proposed Side Elevation (ELE B) Scale 1:2 A B C All dimensions to be checked on site. Figured dimensions to be read in preference to scaled. KDP accepts no responsibilty for any unauthorised amendments to the drawing and does not permit unauthorised copying of the drawing. This drawing is copyright and remains the property of KDP unless otherwise agreed SCHEME REVISED SCHEME REVISED Scheme Revised following comments from LPA CW CW THE KEITH DAVIDSON PARTNERSHIP CHARTERED ARCHITECTS - PROJECT MANAGEMENT - 3D VISUALISATION 13 Seymour Terrace Seymour Street Liverpool L3 5PE Telephone: +44 () Facsimile: +44 () info@kdparchitects.com Website: Planning Client Job number Job title Drawing number Eastbay Close, Cardiff CF14BA Drawing title Proposed Elevations (1) Revision 1437 C 3 Scale Drawn 1:2@A1 CW Checked Date

14 RVW Consulting Limited 7. TAN 15 DEVELOPMENT ADVICE MAP AND FLOOD LEVEL INFORMATION Project Number C6622

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16 ATI-12426a Student Development, East Bay Close, Cardiff E: N: Current Flood Map Figure 1 shows the current Flood Map (version 2171) at this location. The Flood Map represents the undefended fluvial and tidal flood extents derived from a combination of detailed and generalised modelled data. The current tidal Flood Map in this area is derived from a mapping study undertaken by Atkins in 28 (ref 1). This study uses sea levels at discrete node locations within the Severn Estuary, based on ABP research undertaken in The levels were projected in-land over a digital terrain model to produce tidal mapped outlines for both the.5% (1 in 2) AEP (annual exceedance probability) and the.1% (1 in 1) AEP. More information on the Flood Map can be obtained from the Natural Resources Wales website 2. Extreme Sea Levels & Climate Change Guidance In February 211, extreme sea levels used in this model were superseded by a nationally consistent set of extreme sea levels (ref 2). These levels were derived using a tidal model calibrated to UK tidal gauge data. The model output is provided for node locations spaced at approximately 2km. 95% confidence bounds for these values were also derived using the confidence intervals for each node location. The extreme sea levels comprise still water level including storm surge, however they do not account for local wave action. The baseline estimations are for the year 28, so climate change is calculated relative to this year, for example add 1.5mm for the year 211. Extreme sea levels for the node points closest to the site location are included in Table 1 for a range of return periods (events) e.g. T1 is the 1 in 1 year return period tide, which is equivalent to the 1% AEP (Annual Exceedance Probability). The node locations are shown in Figure 3. Table 1 Extreme sea levels for adjacent nodes Node Easting Northing Extreme Event Sea Level (maod) T25 T5 T75 T1 T2 T To provide the estimate of extreme sea levels for the site (Table 2), levels were interpolated from the adjacent nodes. Table 2 Extreme sea levels interpolated between adjacent nodes Extreme Event Sea Level (maod) Node Easting Northing T25 T5 T75 T1 T2 T1 Site % Confidence Bound (+/- m): The current guidance on climate change from DEFRA is as follows: Table 3 Sea level rise, mm per year Assumed vertical land movement

17 The calculated future extreme sea levels are shown in Table 4. Adopting a precautionary approach as advised by Environment Agency guidance (ref 4), these levels include the upper level 95% confidence bound. Table 4 Extreme sea levels for the site (including 95% Confidence Bound) Year Sea level Extreme Event Sea Level (maod) rise(m) T25 T5 T75 T1 T2 T Breach Analysis Results Breach Analysis results are from the Cardiff SFCA (Strategic Flood Consequence Assessment) v2 (ref 5). This was undertaken by Atkins in August 211 (final report issued on 16/8/211). The following information is for indication only and is completely unwarranted. The site is situated in Area I of the Cardiff SFCA (see Appendix A). The most significant flood risk in the east of the area is due to extreme tide levels in the Severn Estuary, the River Rhymney and the Roath Brook. In the west of the area the main risk arises from potential increases in water levels in Cardiff Bay. The risk of breach has been assessed based on methodologies underlying the Environment Agency s Severn Estuary Flood Risk Management Strategy (SEFRMS). The increase in level up the Roath Brook during extreme tide events has been tested by routing a fluvial flood event against a fixed tide level through a NRW 1D HEC RAS model of the Roath Brook and Lower Rhymney. Water levels in the Bay were estimated for extreme tidal and extreme fluvial flood events using a 1D ISIS Bay model. Fluvial inflows to the model were derived from the outflows at the bottom of the EA Ely-Taff ISIS-TUFLOW model. The breach assessment essentially comprises consideration of the joint probability of wave and extreme still water tide levels (SWL), the probability of breach and the consequences of breach events. Different combinations of SWL and wave height, corresponding to a series of joint probabilities were tested for scenarios at each time horizon. Appendix B refers to the different scenarios tested. Breach analysis results for these scenarios include water surface elevation (maod) at the site, and tide level (maod), and are shown in Table 5 below. Table 5 Breach analysis results for the site Scenario CASE1_rev1 CASE11_Sens CASE12_Sens CASE13 CASE14 Model Grid Size (m) Wet Cells 14 Elevation, mean (maod) NULL NULL NULL NULL 8. Elevation, max (maod) NULL NULL NULL NULL 8.17 Depth, mean (m) NULL NULL NULL NULL.14 Depth, max (m) NULL NULL NULL NULL.8 Velocity, mean (m/s) NULL NULL NULL NULL.7 Velocity, max (m/s) NULL NULL NULL NULL.37 *Null values show that the site is flood free for that scenario.

18 The access route provided is shown to be flood free in all modelled scenarios. 4. Additional Information NRW holds no historic flood information for the site or nearby vicinity. The local authority may be able to provide information on issues such as localised flooding from sewers, drains and culverts. 5. References 1. Tidal Flood Mapping Study (Penarth and Chepstow), Study report Issue 1, Atkins July Department for Environment, Food and Rural Affairs, 211. Technical Report Design sea levels. R&D Report SC664. Defra/Environment Agency 3. Flood and Coastal Defence Appraisal Guidance: FCDPAG3 Economic Appraisal. Supplementary Note to Operating Authorities Climate Change Impacts; October 26; Department for Environment, Food and Rural Affairs. 4. Using the national coastal flood boundary data for England and Wales, Environment Agency Operational Instruction 49_11, Issued 4/2/ Cardiff Strategic Flood Consequences Assessment, Phase 2 Part 1 Update Extend Development Lifetime to Areas A, H and I, Final Report, Atkins August Notes Undefended scenarios are provided as being a possible worst case scenario in the event of defence failure. They are used as the basis of the Flood Map. Extreme sea levels provided as part of this project are accurate to one decimal place (Table 4). Two decimal places have been provided to show the gradual change between nodes seen in the model, however, this does not imply greater accuracy. The scope of the model is the mapping of flood risk, it is not intended for detailed design. The model should be considered as the starting point for more detailed modelling, commensurate with the consequences of flooding at the site of interest. NRW models are available under licence agreement for the purpose of further development. Contact Natural Resources Wales at datadistribution@naturalresourceswales.gov.uk for details of terms, conditions and pricing. If the data is used in support of an FCA, please include the reference number. Please refer to NRW standard terms and conditions. Flood Risk Analysis 17/3/217

19 Legend Site Location Flood Zone 3 (1 in 1 year undefended fluvial and 1 in 2 year undefended tidal extents) Flood Zone 2 (1 in 1 year undefended fluvial and tidal extents) Areas benefiting from defences Defences!! Flood Storage Areas Main Rivers Access Project Student Development, East Bay Close, Cardiff, CF1 4BA [Ref: ATI-12426a] Drawing Figure 1: Current Floodmap [v2171] ± Date 17th March 217 Scale 1:5,

20 Legend Site Location Flood Depth (m). -.3 >.3 >.6 >1. >2. Access Project Student Development, East Bay Close, Cardiff, CF1 4BA [Ref: ATI-12426a] Drawing Figure 2: Depth Grid for CASE14.5% AEP (1 in 2) year event (211) ± Date 17th March 217 Scale 1:5,

21 ! ( Legend Site Location _ ^! ( _ ^! (! ( Projection Lines 46 Extreme Sea Level Node Project Student Development, East Bay Close, Cardiff, CF1 4BA [Ref: ATI-12426a] Drawing Figure 3: Extreme Sea Level Node Locations! ( 412 ± Date 17th March 217 Scale 1:3,